In Blender, is there a way to apply boolean to multiple objects at the same time? Or is there an alternative?

Well you could join the objects and then apply the the Boolean modifier. Then separate them if you need to.

From looking thru some resources the suggestion Cybermonk makes is the only way to do what you are asking I am not sure if any of those hard surface modeling add-ons that are for sale can do what you are asking but joining then applying the Boolean Modifier seems the only current option

Why not just select one model, apply a boolean to the second model, then add another boolean modifier and add a third model, etc? I don't see a reason you can't add more than one boolean modifier. Either apply it to the first model then add another one, or select the second, third, etc., and add boolean to those as well. Cybermonk's solution is the most elegant and simple though. I'd go that route first.

Keep in mind, boolean modifiers do screw up the geometry to some degree so adding boolean to tons of objects isn't exactly a great solution, depending on what you're trying to accomplish. If your resulting model will be subdivided, UV unwrapped or deformed in any way, boolean can really mess up the process. It's always best to explore logical ways to model the type of shape you're looking for first, and resort to boolean as the final solution to solve the issue. However, there are some boolean addons that work very well on multiple objects. Have a look at the Bool Tools and also Hard Ops addons. Hard Ops is the best one, but I don't think it's free.

Thanks to everyone for all of your replies.

Just so that everyone knows, the objects I'm working aren't just a few. There are tons and tons of objects, so it's not something that can reasonably be done by going one by one. It's not a "centipede" of objects, so to speak, that directly connect into each other, such as a leg to an ankle, an ankle to a foot, etc. They're all scattered about. I'll attach a picture to make it more clear.

As for the whole boolean modifier situation, if someone could explain exactly how Cybermonk's suggestion would work, I would really appreciate it. I'm a little confused on exactly how that's supposed to work.

You are wanting to boolean all those blocks into one object right? You are going to have to do it one at a time I"m afraid. There is noway to boolean them all together at one time.You can join objects together and then use a boolean modifier on them. However there are issues with that as well. For instance the geometry of the two joined meshes cant overlap. This will cause the boolean modifier to act strangely. I'm afraid there is no easy way to do what you want. I could be wrong though. Good luck.

The issue is that it's pretty much impossible to do it one by one because of the overlapping of all of those different objects. It's the "centipede" example I used.

Is there something besides the boolean that might help in this situation? What I'm trying to do is delete the faces that are inside of the object/inside of each other. Is there some other way to do that?

You can use boolean to do this. It's just gonna be slow going. Select one of the objects and give it a boolean modifier. Set the boolean operation to union and set the object to one that is overlapping. Then apply the boolean modifier. This will join the 2 geometries and delete the inner parts. also the original geometry will be left as a separate object. You'll want to delete that. Now use the new object to boolean another overlapping object. Slow but it will work.

What I would like to know now is if there's another way besides boolean to get this done. Is there?

First posted at 5:24PM Tue, 29 October 2019 - #4368511

What I would like to know now is if there's another way besides boolean to get this done. Is there?

Try the BOOL TOOL addon in Blender. This will allow you to select every object once, and just apply a Union operation. I tried it on 20 duplicate cubes and it worked fine in less than a second using the Auto Boolean feature. Once you install the addon, just press N for the sidepanel. It will appear under the Edit tab. Just quickly select all the cubes (doesn't matter the order) and press Union button. Make sure they are not instances. They have to be copies.

If you're dead set on not using Bool Tool for some reason, or if the operation fails you, then there are only a couple of solutions left that are perhaps less than desireable but may work. First would be to join all the objects as one, then apply a remesh modifier. This may not be a great choice, because in order for it to voxelize the objects together, you'll need an Octree Depth of around 7 or 8 (which will produce a very dense mesh), and a low threshold (around 0.15 or so). If your computer isn't powerful enough, this could very well crash Blender and it may not be the result you are hoping for. However, if you can get that method to work, then you can apply a decimate modifier on top of that to reduce polygons, or just retopologize the mesh.

Correction to my post about Bool Tool... the order of selection does make a difference. In the Scene hierarchy panel, select each object in order. I know you have a lot of objects there, but doing it that way will increase the chances of a successful Union operation. So, if you have Cube, Cube001, Cube002, etc., then select them in that order. That's the only tool I can think of which will allow for this. If not, then the Remeshing or Retopo is the only other way in Blender I can think of.